Iron oxide powder with an average size of particles of 0.2 - 0.3 μm is used for the production of ferrite cores. Mineral and oxidic admixtures or contaminations are decisive for the quality of the endproduct.

Sample preparation:In a nickel melting-pot mix 100 mg of the sample, dried to constant weight at 105 °C, with 8 sodium hydroxide tablets for analysis (1.5 g). Directly with the gas burner heat the covered melting-pot to weak red glow for 30 minutes. After cooling dissolve the content of the melting-pot in water for analysis. For that purpose put the melting-pot with the cover into a glass beaker as well as 30 - 50 ml water for analysis, warm on a bath of water, until the melting cake has dissolved. Adjust the suspension to a pH-value of 7 - 8 with sulfuric acid 25 % (check with Universal indicator strips pH 0 - 14), quantitatively transfer it into a 200-ml standard volumetric flask and fill up to volume with water for analysis. After mixing let the insoluble parts settle and filter the supernatant solution through an ash-free, acid washed filter. A blank reading analysis must be considered, made with the used reagents according to the procedure above.